These sandstone columns were part of the U.S. Capitol before they were installed on the grounds of the National Arboretum.

“I think people walk around the city every day and take its beauty for granted,” says Chris Shaheen of D.C.’s Office of Planning. Washington is known around the world for its parks and vistas, but for those who live here, it’s easy to forget how many outdoor opportunities surround us. Get a reminder Sept. 24-Oct. 1 from WalkingTown DC/BikingTown DC. This year, the annual extravaganza of free tours sponsored by Cultural Tourism DC features the theme of “Green DC,” with hikes, strolls and rides highlighting natural resources. Shaheen’s tour, “D.C.’s Public Space: Transforming the Nation’s Capital from Gritty to Garden City” (Sept. 25, 6-7:30 p.m. and Sept. 29, 11:30 a.m.-1 p.m., 1.5 miles), focuses on how regulating the green area between sidewalks and private property has led to a pleasant streetscape for pedestrians. For details about the week’s 100-plus tours, visit Culturaltourismdc.org. Here are four natural selections.

WALKING TOURS

Canal Park in D.C.’s Riverfront Neighborhood

Sept. 27 and Oct. 1, noon-1 p.m., 0.75 miles

Prepare to put on a hard hat — seriously — because this slice of nature is still under construction. The city’s newest park, slated to open in mid-November, is on the former site of the Washington Canal, which was a critical mode of transportation for much of the 19th century. After the waterway was rendered obsolete by railroads, it was filled in and eventually became a bus depot.

Today, the three-acre plot is being turned into a site for active recreation, featuring large lawns, fountains designed for frolicking and an ice-skating rink, says Chris VanArsdale, executive director of the Canal Park Development Association. He’ll lead tours to give interested folks an early glimpse at what he predicts will be a huge draw to the burgeoning Capitol Riverfront neighborhood.

The Gardens and Grounds of the National Arboretum

Sept. 29, 10 a.m.-noon, 4 miles

Everyone drives by the National Arboretum on New York Avenue, but few people take the time to stop and smell the flowers (except in April and May, when the azalea collection attracts hordes of visitors).

Curator Lynn Batdorf, who’s been caring for flora here for 36 years, points the finger at the word “arboretum.” “The average person doesn’t know what it means,” says Batdorf, who describes the 446-acre site as a zoo for plants. “But they all fall in love with it.”

The tour will begin by heading up Mount Hamilton — one of the highest points in the city — where folks can gander at the view. Then it will wind by the azaleas, a vast meadow, the original sandstone columns from the U.S. Capitol, a trail studded with wild flowers, and more. The finale? “The most formal herb garden you’ll ever see,” Batdorf promises.

BIKING TOURS

Anacostia Riverwalk Trail from Tidal Basin to RFK Stadium

Sept. 30, 8:30-10:30 a.m., 9 miles

Want to take a trip on a scenic trail? “You don’t need to go to Great Falls,” says tour guide Russ Norfleet, who’s been amazed by the Anacostia River’s transformation. He remembers when the water was filled with debris, but recent cleanup efforts have made it quite the looker. “And it doesn’t smell when you get close,” he adds.

It’s now possible to tool around on 12 miles of the trail (which will eventually extend 20 miles from Bladensburg, Md., to the National Mall). Norfleet will show off his favorite part of D.C.: the area along the Southwest Waterfront, with its fish market and houseboat community. From there, he’ll buzz by Buzzard Point and continue through Diamond Teague Park and Yards Park.

The route along the river is also a favorite of wildlife — Norfleet often spies flocks of ducks and other birds among the marshes.

Rock Creek Conservancy Eco Tour

Sept. 29, 9 a.m.-noon, 8 miles

Hanging out in Adams Morgan, you might never suspect you’re just steps from Rock Creek Park. “It’s amazing how many of my kids’ friends don’t know it’s there,” says David Cottingham, president of the Rock Creek Conservancy, which encourages locals to take care of the park and the creek.

One way to get started is on his bike tour, which will begin at Thompson’s Boathouse in Georgetown and wind its way past bridges, the old water gates at the C&O Canal, Peirce Mill (built in the 1820s) and a fish ladder for herring and shad. Cottingham will talk history and explain steps folks can take — both at the park and at home — to keep Rock Creek healthy.

It’ll be a slow trip with several stops, and it will stay in the valley to avoid biking uphill. “We’re going to spend three hours, but you could spend a lifetime there,” Cottingham says.

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